PursuitSpecial
Well-Known Member
A modern fuel crisis calls for modern solutions. Well...sort of modern, for an old, tired car. I used to get about 8 or 9 mpg putting around town and could never quite hit 20 on highway trips in the '81 Gran Fury when I had the holley economaster carb and points ignition. When gas hit $5 a gallon it got a little pricey to cruise around. The car also had severe spark knock issues running 87 octane, but it turned out the gas they're selling as 87 non-ethanol here is absolute garbage and spark knocks and vapor locks in my lawnmower too, so no more of that. The stock ESA computer would probably get the best mileage since it can control timing and fuel based on vacuum and temperature with automatic knock retard, but finding sensors and a compatible thermoquad that still works as intended is probably impossible.
The solution is manual dynamic control over the fuel and timing curves. I used a Holley 4175 that I installed a "mile dial" electronic carburetor kit on, which allows you to lean out the mixture with a knob inside the car controlling a duty cycle solenoid on the main circuit inside the fuel bowl. It can change mixture by about 20%. I jetted it with 52-2 close-limit jets and put a #17 two-stage power valve in it. I had to take the stock knock sensor off to clear the front bowl. For timing control, I'm using an MSD 8981 programmable timing computer, which allows you to set your own timing curve using a locked distributor. I have the base timing set at 40 degrees and it will retard back to 10 degrees at low RPM and advance back to 40 on an adjustable curve. I also installed an MSD engine knock alert to tell when I pick up detonation, using a knock sensor I put in the intake beside the factory hole, and a ZTS-4 driving computer which monitors fuel consumption and calculates instant fuel mileage, so as I cruise down the road I can fine tune my mixture and timing to the point I start to pick up knock and watch how my mileage reacts.
I've been burning 93 octane premium from wal-mart and it's good enough I can lightly cruise around fully leaned out and locked at 40 degrees of timing and never pick up knock past a certain throttle opening, if I need to accelerate quickly I just zero out the initial knob and go back to the standard safe timing curve and richen up the mixture. There's no spark knocking at all with my base curve, which is 10 at idle, starts slowly advancing around 1000 rpm and never maxes all the way to 40, it hits the 4-degree retard chip around 4000 and won't go past 36.
I've put 3 tanks of gas through it so far, my heavy traffic city driving averaged 11.8 mpg, and on the road on a light 60mph cruise it will hit 30mpg. Well into the 30s if I get on the highway at 70 and draft behind an 18-wheeler. The running average after a road trip is currently sitting at 22.1, which is a massive improvement over what it used to get. I verified the accuracy of the fuel meter and driveshaft counter from my computer, the average it's throwing out is within 5% of what the odometer and gps says and what the gas pump says it dispensed. Once I collect more data from the system I can get an exact figure on how much it has improved my overall efficiency, and how much money it saved, once you account for all the money I spent on this stuff...
The solution is manual dynamic control over the fuel and timing curves. I used a Holley 4175 that I installed a "mile dial" electronic carburetor kit on, which allows you to lean out the mixture with a knob inside the car controlling a duty cycle solenoid on the main circuit inside the fuel bowl. It can change mixture by about 20%. I jetted it with 52-2 close-limit jets and put a #17 two-stage power valve in it. I had to take the stock knock sensor off to clear the front bowl. For timing control, I'm using an MSD 8981 programmable timing computer, which allows you to set your own timing curve using a locked distributor. I have the base timing set at 40 degrees and it will retard back to 10 degrees at low RPM and advance back to 40 on an adjustable curve. I also installed an MSD engine knock alert to tell when I pick up detonation, using a knock sensor I put in the intake beside the factory hole, and a ZTS-4 driving computer which monitors fuel consumption and calculates instant fuel mileage, so as I cruise down the road I can fine tune my mixture and timing to the point I start to pick up knock and watch how my mileage reacts.
I've been burning 93 octane premium from wal-mart and it's good enough I can lightly cruise around fully leaned out and locked at 40 degrees of timing and never pick up knock past a certain throttle opening, if I need to accelerate quickly I just zero out the initial knob and go back to the standard safe timing curve and richen up the mixture. There's no spark knocking at all with my base curve, which is 10 at idle, starts slowly advancing around 1000 rpm and never maxes all the way to 40, it hits the 4-degree retard chip around 4000 and won't go past 36.
I've put 3 tanks of gas through it so far, my heavy traffic city driving averaged 11.8 mpg, and on the road on a light 60mph cruise it will hit 30mpg. Well into the 30s if I get on the highway at 70 and draft behind an 18-wheeler. The running average after a road trip is currently sitting at 22.1, which is a massive improvement over what it used to get. I verified the accuracy of the fuel meter and driveshaft counter from my computer, the average it's throwing out is within 5% of what the odometer and gps says and what the gas pump says it dispensed. Once I collect more data from the system I can get an exact figure on how much it has improved my overall efficiency, and how much money it saved, once you account for all the money I spent on this stuff...
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